Explosive arming and firing system



Nov. 7, 1967 C. E. SIMPSON EXPLOSIVE ARMING AND FIRING SYSTEM 5 Sheets-Sheet i Filed Dec. 10, 1965 REMOTE ARM (CLOSED) REMOTE RESET (OPEN) w m s P N m ws m E WAVELENGTH WAVELENGTH ATTORNEY Nov. 7, 1967 c. E. SIMPSON EXPLOSIVE ARMING AND FIRING SYSTEM 3 Sheets-Sheet 2 Filed Dec. 10, 1965 E H T (REMOTE FIRE) o] wzbjwm 8 w FIRING LEVEL INVENTOR. CLARENCE E. SIMPSON I IA ATTORNEY Nov. 7, 1967 c. E. SIMPSON 3,

I EXPLOSIVE ARMING AND FIRING SYSTEM Filed Dec. 10, 1965 3 Sheets-Sheet 5 INVENTOR. CLARENCE E SIMPSON ATTORNEY 3,351,016 EXPLOSIVE ARMING AND BRING SYSTEM Clarence E. Simpson, Glendale, Ariz., assignor to Universal Match Corporation, a corporation of Delaware Filed Dec. 10, 1%5, Ser. No. 512,876 7 Claims. (Cl. 102-70.2)

This application is a continuation in part of my prior filed co-pending application Ser. No. 387,156, filed Aug. 3, 1964, and now abandoned.

The present invention pertains to explosive systems and more particularly to improved systems incorporating a firing chain wherein a number of predetermined events must take place before an explosive is ignited. More particularly, the present invention includes improvements in the explosive arming and firing system disclosed in my said co-pending application.

Modern explosive technology has taught the utilization of a number of systems to insure safety and reliability in the ignition systems of explosives. The term explosive is used herein in the broad sense to include defiagrating and detonating materials and the like. The impact of space technology and missiles has placed demands upon explosive ignition systems to further insure reliability while nevertheless substantially increasing safety requirements.

One prior art approach to the explosives ignition problem is the utilization of a hot wire system wherein a nichrome wire is heated to a temperature sufiicient to ignite an explosive. The hot wire system is an attempt to insure that a deliberate and purposeful current is supplied to the wire and that an accidental transient current will not detonate the explosive. Another firing technique is the utilization of an exploding wire wherein a high-voltage and high-current (over a small period of time) is forced through a wire to produce vaporization of the wire with a subsequent shock wave of suflicient magnitude to detonate the explosive. Both the hot wire system and the exploding wire system nevertheless require gating and it is in the gating of appropriate signals that difiiculty arises; in addition, the high-voltage and current requirements of the exploding wire techniques militates against the utilization of a remote power source for applying the necessary current and voltage to the wire.

A variety of systems and circuits have been devised for energizing the actual hot wire or exploding wire firing element; these systems depend for reliability upon sophisticated and complicated techniques. One of the common types of gating systems used implements the energization of the firing mechanism by use of a radio-frequency signal having a predetermined frequency or frequencies. RF filters are utilized on the firing devices to insure thatspurious radio signals do not inadvertently fire the explosive. In some instances, the coding techniques extend to the utilization of phase, frequency, or even amplitude modulation to insure that stray frequencies, being emitted by the high density electronic signaling and control components usually found in a missile device, do not inadvertently instigate the necessary chain reaction to ignite the explosive. Still another element that is sometimes utilized in the firing chain of an explosive ignition system is the utilization of a mechanical barrier between the actual firing current being applied to a hot wire or exploding wire and the explosive. The physical displacement of a portion of a conductor or the physical displacement of another element in the firing chain greatly adds to the technical difiiculties and detracts from the reliability so necessary in a modern missile system. A variety of other types of gating systems and firing chains have been used in the prior art; however, existing systems disc nevertheless exhibit poor reliability both from a protective and from a total systems reliability standpoint. The present systems are costly, bulky, heavy, and since they are complicated and sophisticated, usually suffer from unreliability.

Accordingly, it is an object of the present invention to provide a unique combination of elements in a firing chain for use in an explosive ignition system.

It is still another object of the present invention to provide an explosives ignition system having the utmost in reliability while nevertheless remaining light, uncomplicated and inexpensive.

It is also an object of the present invention to provide a firing chain for use in an explosives ignition system including elements operable in response to light.

It is another object of the present invention to use light stimuli for firing, gating, tripping, arming, sequencing, or locking-out an explosives system.

Further objects and advantages of the present invention will become apparent as the description thereof proceeds.

In accordance with the present invention, a photosensitive device having an electrical characteristic variable in accordance with variations in light directed thereupon is utilized to gate a sufllcient current in an electrical circuit to fire an explosive when a light stimuli is applied thereto. The use of light stimuli as an element in a firing chain of an explosives ignition system alleviates a substantial amount of sophistication such as complicated electronics which would ordinarily be necessary and, concurrently, actually increases the reliability and substantially improves the safety of the system.

In the presently preferred embodiment of the invention, the photosensitive device performs the dual function of gating current in the circuit and actually igniting the explosive. In this embodiment, the photosensitive device is embedded in the explosive and positioned to receive light transmitted from a light source.

In accordance with another embodiment of the invention, the photosensitive device is connected in the electrical circuit but merely gates the current to an orthodox ignition element such as a hot wire. In this embodiment, the hot wire is embedded in the explosive and the photosensitive device may be positioned remote from the explosive and the ignition element.

In both embodiments, the light stimuli is preferably controlled and directed upon the photosensitive device by means of a light-transmitting rod such as a fibrous plastic cylinder extending between a light source and the photosensitive device with appropriate shielding provided to prevent stray light from reaching the photosensitive device.

The invention may more readily be described by reference to the accompanying drawings in which:

FIGURE 1 is a schematic illustration of a firing chain implementing the teachings of the present invention utilizing a photosensitive device positioned remote from the explosive and a hot wire igniter.

FIGURE 2 represents simplified drawings of curves useful in the explanation of the operation of the system of FIGURE 1.

FIGURE 3 is a schematic circuit diagram of the equivalent circuits of the firing chain of FIGURE 1.

FIGURE 4 represents a schematic firing chain utilizing another embodiment of the present invention.

FIGURE 5 represents a simplified curve useful in the explanation of the operation of the firing chain of FIG- URE 4.

FIGURE 6 represents simplified curves useful in the description of operation of the system of FIGURE 4.

FIGURE 7 is a schematic illustration of a firing chain implementing the teachings of the present invention showing the presently preferred embodiment wherein the photosensitive device is embedded in the explosive, performing the dual function of a current gating element and an ignition element.

FIGURE 8 is an external perspective view of an apparatus embodying the present invention attached to an explosive charge.

FIGURE 9 is a sectional view of the apparatus of FIG- URE 8 incorporating the preferred embodiment of FIG- URE 7.

Referring to FIGURE 1, an explosive charge 10 is shown and is partly broken away to show a hot Wire 11 embedded therein. One side of the hot wire is connected through conductor 12 and through a photosensitive device '13 to ground. The other side of the hot wire 11 is connected through conductor 15 through photosensitive device 16 to conductor 17. In the embodiment chosen for illustration in FIGURE 1, the photosensitive devices 13 and 16 are photo-resistive; that is, each of the devices represents a very high resistance (measured in megohms) when no light impinges on the device, while the resistance drops to a very low value (measured in terms of ohms) when light is directed upon the device. Thus, the series resistance of the two photosensitive devices 13 and 16 and the hot wire 11 is extremely high when no light is directed upon the devices 13 and 16; however, when light impinges on the devices 13 and 16, the series resistance of the photosensitive devices and the hot wire becomes very low.

A light source such as a lamp is mounted within a parabolic reflector 26 to direct light axially of a fibrous, molecularly oriented, light-transmitting plastic cylinder 27. The light transmitted by the lamp 25 is thus carried through the cylinder 27 to the photosensitive devices 13 and 16. The lamp 25 may be energized from any convenient source of current 30 and, in the embodiment chosen for illustration in FIGURE 1, is placed in series with switches 31 and 32. Since the embodiment in FIGURE 1 utilizes the light system as the last element in the firing chain, a plurality of switches such as switches 31 and 32, connected in series, are used to insure that any firing signal is deliberate and not accidental. The arming portion of the embodiment of FIGURE 1 utilizes a pair of siliconcontrolled rectifiers and 41 connected to a power supply, indicated in FIGURE 1 as a current source 42, and connected to a gating signal system 45. The gating signal system 45 receives RF signals from a transmitter which is energized through an arming switch 51.

Operation of the embodiment of FIGURE 1 may be described as follows. When the explosive device is to be placed in readiness for firing, the arming swtich 51 is closed and the transmitter 50 subsequently emits radio frequency signals to be received by the gating signal system 45.-The arming signal is thus applied to the gate electrode of the silicon-controlled rectifier 40 thus permitting current to flow from ground through the series-connected photosensitive devices 13 and 16 and hot wire 11 through the silicon-controlled rectifier 41 to the current source 42. The system is thus armed and the extremely high resistance of the photosensitive devices 13 and 16 prevent sufiicient current from flowing through the hot wire 11 to raise the temperature thereof to the extent necessary to ignite the explosive charge 10. If, subsequent to arming, it is decided to dis-arm the system, the arming switch 51 is opened and the radio frequency signals transmitted by the transmitter 50 cease. The gating signal system 45 thus applies a reset signal to the gate electrode of the sili con-controlled rectifier 41. The capacitor connected between the anodes of the silicon-controlled rectifier has previously become charged; subsequently, with the initiation of current conduction in the silicon-controlled rectifier 41 the instantaneous voltage applied to the anode electrode of the silicon-controlled rectifier 40 will be below ground potential and, assuming that the RC time constant is long enough, the silicon-controlled rectifier 40 will be cut off and the arming system will be reset. When the system is in its reset condition, the closure of firing switches 31 and 32, with the subsequent energization of the lamp 25, will not effect a firing of the explosive charge 10; rather, the change in the electrical resistance of photosensitive devices 13 and 16 will be of no consequence since the current source supplying current to the hot wire 11 (silicon-controlled rectifier 40) will be disarrned. Assuming that it is desired to arm and fire the explosive charge 10, the arming switch 51 may be closed with subsequent application of the current source 42 to the hot wire 11 through the silicon-controlled rectifier 40 as described previously. Switches 31 and 32 may be then closed to initiate the firing action. The lamp 25 thus generates sufficient radiation to be transmitted through the cylinder 27 to the photosensitive devices 13 and 16. The subsequent radical drop in resistance values of the series-connected photosensitive devices 13 and 16 drastically reduces the circuit resistance in series with the hot wire 11. The drop in resistance results in a substantial current increase thus appropriately raising the temperature of the hot wire to ignite the grain 10. It may be seen that the utilization of the light system element in the firing chain is substantially impervious to normal hazards encountered by electronic actuated systems. The light-transmitting fibrous cylinder 27 will normally be shielded (although shielding may not be neceessary) and may be located remote from the photosensitive devices 13 and 16. Stray RF signals will have no effect on the light-transmitting system thereby eliminating the possibility of accidental firing due to spurious or stray radiation. Although stray RF signals may cause the arming system of the embodiment shown in FIGURE 1 to arm the device, the devices will nevertheless be prevented from being fired since no stray radiation can induce a sufiicient chang in the resistance of the photosensitive devices to enable current of appropriate magnitude to pass through the hot wire 11. The photosensitive devices 13 and 16 are shown in the embodiment in FIGURE 1 as embedded wtihin and forming an integral part of the cylinder 27. There are a number of arrangements that may be utilized to implement the impingement of light transmitted through the plastic onto the appropriate surfaces of the photosensitive elements, the arrangement shown in FIGURE 1 merely being schematic.

The light source and the photosensitive device may be matched so that further safety provisions may be made through the appropriate selection of radiation frequencies. For example, referring to FIGURE 2, a schematic curve is shown comparing relative radiant power density to wave lengths of a chosen source. It may be seen that the light source emits a continuous spectrum of wave lengths; however, a peak power density of radiant energy is emitted by the light source at a wave length of t This particular wave length may be chosen to correspond to an appropriately optically filtered receiving wave length of the photosensitive devices. The second curve shown in FIGURE 2 compares relative resistance of a photoresistance device to wave length of light impinging on the device. The schematic curve showing this relationship in FIGURE 2 is chosen so that the peak sensitivity of the photo-resistor device occurs at a wave length equal to )i which corresponds to the peak relative radiant power density emitted by the light source. Thus, an additional safety factor may be entered into the light system in that a substantial power density of a particular wave length may be necessary to sufficiently change the electrical characteristics of the photosensitive device to fire the explosive. Utilizing the concept of the present invention, it is possible to arrive at a system utilizing emitted light from a radiation source quite remote from the explosives ignition system. For example, a space vehicle may be triggered (stage firing, course charge firing, etc.), upon sensing a predetermined radiation source such as receipt of radiation of appropriate radiation power density and wave length from the sun. Light may thus be directed by a lens system, optical piping, or mere orientation of the light source such as the previously described sun radiation.

The equivalent electrical circuit of the firing chain of FIGURE 1 is very simple and is shown in FIGURE 3. The current source 60 is shown connected in series with an arming switch 61, the hot wire 62, and a pair of variable resistances 63. The variable resistances 63 represent the photo-resistant devices 13 and 16 which simultaneously change electrical resistance when light impinges thereon. It will be understood that the photo-resistive devices 13 and 16 may be replaced by photovoltaic or current-generating light-sensitive devices thereby eliminating the necessity of a current source 60. It is possible to provide a plurality of series-connected currentgenerating photosensitive devices in such a manner as to provide a power supply to energize the hot wire of an ignition system merely upon the receipt of sufiicient light of appropriate wave length. As mentioned previously, the fibrous plastic or glass light-transmitting cylinder may not be necessary in some instances in that the light may be transmitted directly onto the surfaces of the photosensitive devices without piping. For example, in such applications as missile technology, it is entirely possible that the ultimate firing of the missile system can take place without electrical connection to the missile. A high intensity light source, of a predetermined wave length (with the use of appropriate filter optics, coherent light, such as generated through LASER techniques, may be used) may be focused on a Window in the missile skin to thereby gate suflicient current to an ignition system within the missile; alternatively, light directed through a window in a missiles skin may be used to arm a missile before launching.

Referring to FIGURE 4, a modification of the present invention is shown utilizing light gating to arm rather than to fire an explosives system. A lamp 80 is enclosed within an appropriate parabolic shield 81 and is connected in series with a current source 82 and an arming switch 83. Thus, the lamp 80 will be energized upon the closure of the switch 83. The light emitted by the lamp 80 is focused by the parabolic refiector 81 onto a light chopper which may take the form of any well-known light-interrupting system. The resulting output of the light chopper 85 is a series of light pulses transmitted through the light-transmitting cylinder 86 to a lightutilization system 87. The system 87 may comprise a plurality of photo-resistive devices such as the type described in connection with FIGURE 1. A large number of photo-resistive devices may be used to provide an even greater radical change in resistance upon receipt of a light pulse. Firing current for the hot wire 88 is provided in any conventional manner and is illustrated in FIGURE 4 basically as a gated power source 90 gating the current from a current source 91 in accordance with RF signals received from a transmitter 92. The transmitter 92 is gated by series-connected firing switches 94 and 95 connected to a power supply indicated in FIG- URE 4 at 96. It will be understood that prior art techniques such as frequency, phase, or amplitude modulation may be utilized on the RF signal to be transmitted by the transmitter 92. Further, appropriate coding techniques may also be utilized, it being understood, however, that the firing chain including these prior art techniques also include the present concept of light stimuli as a series element in the firing chain. To further explain the operation of the system of FIGURE 4, reference will now be had to FIGURES 5 and 6. The light pulse provided by the chopper 85 is represented, to an enlarged scale, in FIGURE 5. The pulse is a relatively short, highamplitude, light pulse transmitted to the photosensitive devices. Any spurious signals or random transient currents generated by the device 90 and subsequently ap- 6 plied to the firing chain will only ignite and fire the system if a light pulse is received by the photosensitive devices concurrently with the receipt of the firing current. This operation is illustrated by the curves of FIGURE 6 wherein it is shown that the transmitted light (the same light pulses shown in FIGURE 5 to a much smaller scale) is received periodically by the photosensitive devices. The second curve of FIGURE 6 illustrates signal amplitude being transmitted in the conductor of the firing circuit. It may be seen that spurious signals and 101 are randomly, and inadvertently, transmitted to the firing chain. The spurious signal 100 is of insufiicient amplitude to fire the explosives system; however, the signal 101 includes a transient spike that would normally be of sufficient amplitude to ignite the explosive and prematurely fire the system. Since the light pulse was not received by the photosensitive devices concurrently with the transient spike, the exceedingly high resistance of the firing chain precludes the initiation of any ignition action; therefore, the system cannot fire unless it is first armed by light transmission. When a firing signal, represented as the signal wave form 102 is applied to the firing chain, the signal reaches an appropriate firing level that would normally actuate the firing system; however, this signal amplitude must be maintained until the next light pulse is received by the firing chain. The conjunctive action of the light pulse and appropriate signal amplitude will then fire the explosive system. It may therefore be seen that the light stimuli utilized in the firing chain, as taught by the present invention, operates as an active element in the firing chain to actuate (ignite or enable) the explosive ignition system. A variety of systems utilizing the present concept may be designed including refinements regarding wave length (0.1225 microns have been found appropriate in the implirnentation of the present invention-1200-250,000 Angstrom units) as well as variations in methods for directing light (molecularly oriented plastic, lens optics, etc.).

Referring to FIGURE 7, illustrating schematically the presently preferred embodiment of the invention, an explosive charge 105 is shown and is partly broken away to show the photosensitive device 106, which also performs the function of an igniting element, embedded in the eX- plosive charge 105. As shown in FIGURE 7, the photosensitive device 106 is a photoresistive element connected in series by means of conductors 107 and 107a to a power supply 108 such as, for example, power supplies as illustrated schematically in FIGURES 1 and 4. The series resistance of the photo-resistive device 106 is extremely high when no light is directed thereupon; however, when light impinges on the photo-resistive device 106, the series resistance thereof is lowered sufliciently to permit an igniting current to flow through the photo-resistive device 106 from the power supply 108, thereby heating the photoresistive device 106 sufiiciently to cause ignition of the explosive charge.

A light source such as a lamp 109 is mounted within a parabolic reflector 110 to direct light axially of a fibrous, molecularly oriented, light-transmitting plastic cylinder 111. The light transmitted by the lamp 109 is thus carried through the cylinder 111 to the photosensitive device 106. The light 109 is energized from any convenient source of current and may be provided with appropriate seriesconnected switches such as shown in FIGURE 1 to prevent accidental firing of the device.

FIGURE 8 illustrates an apparatus generally indicated by reference numeral 115 embodying the present invention. The assembly comprises a housing 116 which is threadedly connected to the main charge 117a. The lighttransmitting element 117 enters the bottom of the housing 116; the conductors 107 and 107a (see FIGURE 7) are carried in a suitable cable 118 afiixed to the housing 116 by means of a suitable threaded connector 119.

FIGURE 9 is a sectional view of the apparatus of FIG- URE 8 incorporating the preferred embodiment illustrated schematically in FIGURE 7. The apparatus comprises a housing 116 provided with a threaded neck 121 for connection to the container 11711 of a main explosive charge. The photo-resistive device 122 is supported by a glass plug 123 received in the housing 116 and retained therein by a glass-to-metal seal 124. The conductors 107 and 107a connected to the photo-resistive device are embedded in the glass plug 123, the leads being received in a threaded connector 125 for connection to the power supply. The lower portion 11611 of the housing, threadedly engaged to the upper portion 116, is provided with an opening which receives the light-transmitting element 117, a suitable grommet 126 being provided to properly position the light-transmitting element 117 to direct light through the glass plug 123 onto the surface of the photo-resistive element 122. When light is directed upon the surface of the photo-resistive element 122, thereby gating an igniting current through the photo-resistor 122, sufiicient heat is generated to ignite the explosive mix 127 which, in turn, initiates the main charge.

The concept of the present invention has been described in terms of gating an arming signal or gating a firing signal; however, the utilization of light stimuli may also be utilized as a lock-out means wherein light stimuli is used to interrupt a firing chain thus insuring passivation of the explosives ignition system. A typical application of light stimuli as a lock-out element in a firing chain is the use of light stimuli (automatically in such cases as the use of radiation from aircraft landing lights) by the pilot or commander of an airborne defense system when the vehicle approaches landing or docking.

It will therefore become apparent to those skilled in the art that the utilization of light stimuli in a firing chain for an explosive ignition system represents a unique approach to solving the difliculties of reliability, safety, and complexity problems of explosive ignition systems presently experienced when using prior art firing chain techniques.

Having described my invention and the preferred embodiments thereof, I claim:

1. An ignition system for explosives comprising:

(a) electrical igniting means in contact with an explosive for actuating said explosive, said electrical igniting means consisting of photosensitive means having an electrical characteristic variable in accordance with variations in light directed thereon;

(b) means for controlling light directed upon said photosensitive means; and

(c) an electrical circuit, including said igniting means, having a characteristic variable in accordance with the electrical characteristic of said photosensitive means.

2. Ignition system of claim 1 wherein said photosensitive means are photo-resistive.

3. An ignition system for explosives comprising:

(a) a source of light;

(b) electrical igniting means in contact with an explosive for actuating said explosive, said electrical igniting means consisting of a photo-resistive device having a resistance variable in accordance with variations in light directed thereon;

(c) means for controlling light directed from said light source to said photo-resistive device; and

(d) an electrical circuit, including said igniting means,

having a characteristic variable in accordance with the resistance of said photo-resistive device.

4. An ignition system for explosives comprising:

(a) a housing containing an explosive at one end there- (b) electrical igniting means in contact with said explosive for actuating said explosive and comprising photosensitive means having an electrical characteristic variable in accordance with variations in light 10 directed thereon;

(c) a solid light-transmitting plug in contact with sa1d photosensitive means, said plug sealed within said housing;

(d) means for controlling light directed upon said photosensitive means through said light-transmitting plug; and

(e) an electrical circuit, including electrical conductors extending through said plug and including said igniting means, having a characteristic variable in accordance with the electrical characteristic of said photosensitive means.

5. An ignition system for explosives comprising:

(a) a controllable source of light;

(b) a secondary explosive charge;

(c) a photosensitive device in contact with said secondary explosive charge, said photosensitive device having an electrical characteristic variable in accordance with variations in light directed thereon for igniting said secondary explosive charge when an igniting electrical current flows therethrough;

(d) means for transmitting light from said controllable light source to said photosensitive device;

(e) an electrical power supply; and

(f) an electrical circuit including said photosensitive device and said electrical power supply, said circuit having an electrical current characteristic variable in accordance with the electrical characteristic of said photosensitive device whereby an igniting current flows through said photosensitive device when an actuating intensity of light is directed thereupon from said controllable source of light.

6. Ignition system of claim 5 wherein said photosensitive device is a photo-resistive device.

7. A system for igniting a heat-sensitive explosive composition comprising:

(a) a heat-sensitive explosive charge;

(b) a photo-resistive resistance heating element in contact with said heat-sensitive charge responsive to a predetermined amount of light for igniting said composition;

(0) means for controlling the amount of light falling upon said photo-resistive heating element; and

(d) an electrical circuit including a power supply and said photo-resistive heating element.

' References Cited UNITED STATES PATENTS 2,927,213 3/1960 Marion et al 102-70.2 3,228,337 1/1966 Grantham et al 102--70.2 3,269,315 8/1966 Gauld 102-702 BENJAMIN A. BORCHELT, Primary Examiner.

W. C. ROCH, Assistant Examiner. 

7. A SYSTEM FOR IGNITING A HEAT-SENSITIVE EXPLOSIVE COMPOSITION COMPRISING: (A) A HEAT-SENSITIVE EXPLOSIVE CHARGE; (B) A PHOTO-RESISTIVE RESISTANCE HEATING ELEMENT IN CONTACT WITH SAID HEAT-SENSITIVE CHARGE RESPONSIVE TO A PREDETERMINED AMOUNT OF LIGHT FOR IGNITING SAID COMPOSITION; (C) MEANS FOR CONTROLLING THE AMOUNT OF LIGHT FALLING UPON SAID PHOTO-RESISTIVE HEATING ELEMENT; AND (D) AN ELECTRICAL CIRCUIT INCLUDING A POWER SUPPLY AND SAID PHOTO-RESISTIVE HEATING ELEMENT. 